The present invention relates to a radiological scaling device which enables the actual anatomical size of a given structure on a radiological image such as an X-ray image to be accurately calculated.
Currently, it is difficult to determine the actual anatomic size of a given structure on an X-ray image. The determination of the actual anatomic size of a given structure is particularly important in fluoroscopy, wherein a procedure is carried out by a physician in coordination with continuous X-ray imaging of the patient.
In fluoroscopy, an image will often be magnified on a screen to aid a physician in seeing small catheters or structures. Measuring the apparent size of an object on a magnified X-ray image will often yield a falsely enlarged value. In particular, when an object-to-film distance is varied so as to accommodate for different sized patients, the size of an object on an X-ray image is increased or decreased, much like the size of a hand shadow on a movie screen is increased or decreased by varying the distance of the hand from the screen.
Many interventional radiology procedures require accurate determination of the size of different anatomic structures. For example, angioplasty and/or stent placement in blood vessels, bile ducts or bronchi require appropriate size determinations of these structures. These structures as well as different types of pathology such as aneurysms, tumors, and strictures are currently difficult to quantitatively measure.
Presently, physicians typically rely on past experience to judge the size of an anatomic structure, which often leads to inaccurate determinations. Alternatively, a "marker" catheter having two small radio-opaque markers spaced approximately two centimeters apart may be used to determine the size of an anatomic structure by a direct arithmetic proportional calculation based upon observed apparent lengths. However, there are several problems with the conventional marker catheter. First, it is often difficult to include both the markers and the anatomic region of interest on the same X-ray image during a procedure. Second, because the conventional marker catheter does not have any mechanism for ensuring that a line extending between the two markers is aligned perpendicular to the X-ray beam, angulation of the X-ray beam can foreshorten the apparent distance between the two markers on the X-ray image, resulting in an inaccurate determination of the size of the anatomic structure in question. Third, the conventional marker catheter is designed for intravascular use, and ignores biliary and bronchial applications. And lastly, a physician may begin a procedure with an unmarked catheter and may not realize until the procedure is already under way that it is desirable to measure a size of a structure, in which case it becomes difficult, time-consuming and expensive to exchange an unmarked catheter for a marker catheter.
U.S. Pat. No. 5,216,700 discloses a tape having a graduated scale with a flexible rib for providing location indicia during an X-ray process. This patent, however, does not disclose using such a tape for sizing structures, and inaccurate results would be generated if this tape were used for sizing structures. That is, because the tape disclosed in U.S. Pat. No. 5,216,700 conforms to the curves of the body and because no mechanism is provided for ensuring that the tape is always perpendicular to the X-ray beam, the apparent length of the device on the X-ray image could be foreshortened.
U.S. Pat. No. 4,850,866 discloses a method and apparatus for measuring the length of the root canal of a tooth by placing a probe of known length into the canal and making an X-ray exposure thereof. However, this technique also does not ensure that the probe is positioned perpendicular to the X-ray beam, so that inaccurate results may again be generated.